The Home Grower's Guide To The Best Soil For Cannabis

Growing cannabis in soil is a great and natural way to crop fat, flavoursome buds. Moreover, soil is perhaps the most forgiving medium in comparison with hydroponic substrates. We break down the best soils for cannabis cultivation so you won’t get mixed up. This blog has need-to-know info for organic growers.

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15 Mar 2018

WHAT’S THE BEST DIRT FOR GROWING WEED?

The answer depends on a number of critical factors of outdoor cannabis cultivation. First, you need to choose a suitable strain for the climate. Then, you must answer the question: to dig or not to dig? It’s important to get into the specifics before you rush into ploughing a field. Balcony growers are probably best-off using pots and containers that can be moved easily, while a sun-drenched, secluded weed plantation may require serious earthworks to create a fertile super soil. Always take care to maintain a pH of 6.0–7.0 for any soil grow.

PHOTOPERIOD VS AUTOFLOWERING

Many cannabis super soil recipes are unsuitable for autoflowering strains. In fact, the best custom super soils are strain-specific. This perfect mix can really only be developed with many years of experience cultivating the same strain, usually continued season after season by taking cuttings. It takes time to build up colonies of beneficial mycorrhizae and a truly living soil. Furthermore, super soils are such a nutrient-rich medium, they’re really only a viable option for experienced organic growers of photoperiod strains. Don’t get it twisted. We love super soil, but it’s a long-term investment, rather than a quick win.

In contrast, autoflowering cannabis strains prefer a light to non-fertilised soil mix. Super soils contain far too high a dose of nutrients for autos. A 50–50 mix of coco coir and light peat-based soil with plenty of perlite for drainage is recommended for autoflowering and young photoperiod plants. It’s always best to go easy on the fertiliser during the seedling stage for any kind of cannabis.

You can get started using small 1–6l pots and transplant into more fertile ground or larger containers of heavier soil after a couple of weeks. Too many nutes too soon invariably leads to over-fertilised, burnt, and stunted plants.

STORE BOUGHT VS HOMEMADE

For the beginner grower, cannabis-specific soil from the local grow store is definitely the best soil. Even grand master organic growers use store bought soils. Of course, you can make some amendments, but many are good to grow right out of the bag. A simple rule of thumb is to add 10–30% more perlite for increased drainage, especially if you plan to supplement heavily with liquid nutrients.

Homemade soil mixes will still probably require you to make a supply run to the grow store. Adding 30% coco coir to a soil mix to increase aeration is advantageous to the root zone. Compressed coco bricks that need to be rehydrated or bags of coco coir fibre are inexpensive and lightweight to carry compared with 50l sacks of soil.

Bat guano is an excellent and inexpensive organic fertiliser for flowering marijuana. Moreover, guano can be added to a soil mix or spread on the topsoil and watered in later. However, manure is not for every grower. Enter Easy Boost Organic Nutrition time-release nutrient pellets. You can add a cup of these to a soil mix to feed plants for the whole life cycle. 100g is enough for 2–3 cannabis plants. Just add water—it couldn’t be simpler. Plus, you can still supplement with a nutrient solution if you happen to be farming vigorous, heavy feeding hybrids.

NO-TILL CULTIVATION

No-till cannabis cultivation is another long-term project. Essentially, this grow-style is all about minimal disturbance to a living soil to preserve the beneficial microbes living in the root zone. This practice can also be applied to containers, although you do need to remove the bulk of the root mass and fill the hole back in with fresh soil. The rest of the roots will decompose.

Re-using soil crop after crop without any additional inputs is how no-till works, in theory that is. However, in practice, it helps to supplement with organic liquid fertilisers. Cannabis plants, just like any other crop, will deplete the nutrients in soil. Weeding is also recommended. Nothing should be competing with your cannabis plants for resources.

AMENDMENTS FOR DROUGHT CONDITIONS

Take a tip from the crafty guerrilla growers of southern Spain and don’t let drought conditions deter you from outdoor cannabis cultivation. You can effectively prep your soil for drought by using water-absorbent polymers. These can be sourced from the hydroponics store or cut free from diapers/nappies in a pinch.

If you expect to encounter extended periods of hot dry weather and you can’t make daily trips to see your plants, water-absorbent polymers can feed your plants. First, dig a hole about 60cm deep and 30cm in diameter. Next, add a few cups of polymer crystals to the bottom of the soil mix, ideally pre-soaked in a light nutrient solution, and cover with the rest of the soil. Transplant your little sprout and water. Later on in the grow, the roots will reach this life-saving reservoir.

Finally, it’s important to remember that soil really is alive. So please avoid cooking the root zone with excessively high temperatures. If you are growing outdoors this summer, use white plastic pots, or better still, Air-Pots and Smart-Pots to help keep the root zone cool. Alternatively, you can create some natural shade for the ganja roots by adding a layer of dry straw to topsoil.